Static electricity buildup can be a problem in both office and factory environments. In the office environment, static buildup can occur simply as a result of an occupant using a chair or other equipment. In a factory environment, static buildup can be a problem in certain types of equipment. In particular, the buildup of static electricity can be a problem in environments where computers, computerized equipment, electronic devices, or similar equipment is being either assembled or used.
It is, therefore, desirable to ground the object being supported so as to permit continuous discharge of static electricity and, thereby, prevent the buildup of an electrical charge. Continuous discharge is particularly important where the object, be it furniture or equipment, is movably mounted on casters.
Several caster devices have been developed to ground a chair leg and permit electrical discharge. For example, the U.S. Pat. No. 619,896, to Lee, issued Feb. 21, 1899, discloses a U-shaped metallic bail adapted to be mounted to the forks of a caster so as to trail along the floor behind the caster. The U.S. Pat. No. 608,234, to Slayton, also discloses a metallic contact arm adapted to be mounted to a prong of a fork which supports a caster wheel. The U.S. Pat. No. 2,533,403, to Schultz, also discloses a metallic link which is oval-shaped and mounted to one side of a caster wheel. Each of these devices, however, is susceptible to the buildup of wax, dirt, or other foreign matter which can render the electrical discharge function ineffective.
Certain devices have utilized means other than conductive members to ground the movable object. For example, the U.S. Pat. No. 2,324,589, to Lytle, discloses a conductive wheel having a spiral link embedded within a web thereof so as to conductively connect the rim of the wheel to the hub. Similarly, the U.S. Pat. No. 2,267,503, to Lytle, discloses a conductive wheel rim which is coated with a thermostat conductive powder.
The U.S. Pat. No. 2,818,534, to Horne, is directed to a conductive bonding arrangement to bond chair legs and tables to a floor surface in a manner so as to avoid buildup of static electricity. The patent describes a bonding arrangement having a sealed ceramic transistor, mounting plates, shunt wires between the mounting plates and buses contacting the floor surface to provide a conductive path. FIG. 8 of the Horne patent shows the use of casters, but those casters do not comprise any portion of the conductive path, and the conductive bonding arrangement is completely separate from the caster assemblies. The Lytle patents, together with the U.S. Pat. No. 2,686,891, to Burgin, describe rolling conductive elements which tend to buildup wax, dirt, or other films of insulative material. Electrically conductive casters, such as those disclosed in Gross Stabil Corporation catalog (333 Race Street, P.O. Box 368, Cold water, Mich. 49036), also disclose this type of rolling conductive contact.